The present invention pertains to a control mechanism for the ignition system of an internal combustion engine and more particularly to a means for interrupting ignition current in a motorcycle engine during transmission shifts.
Motorcycle transmissions in general share several broad similarities from model to model and make to make. Almost all motorcycle transmissions are activated by a foot pedal, shifts being made by raising the foot pedal from its rest position to its uppermost position and allowing it to return to rest after the shift is completed. Downshifting is performed by depressing the pedal.
Motorcycle transmissions are almost universally constant mesh transmissions. In these transmissions the outside surfaces or teeth of the gears are always engaged and specific gear selections are engaged by dogs on the sides of gears and gear assemblies which are slid along the transmission shafts by yokes connected to a shifting drum. This shifting drum is turned through an activation mechanism by the movement of the shifting pedal.
In order to effect shifting, it is necessary to remove the mechanical load from the transmission. This is normally accomplished with a clutch mechanism which mechanically disconnects the engine from the transmission when the clutch handle is pulled thereby mechanically unloading the transmission.
Attempts have been made in the past to improve on the shifting mechanism by incorporating means to unload the transmission into the shifting mechanism itself. In these systems shifting is performed by simply moving the foot pedal without the need to operate the clutch lever. These systems employ electro-mechanical switches which interrupt current to the ignition circuit of the engine when the shifting mechanism is activated. With ignition current interrupted, the engine no longer applies torque to the transmission thereby unloading it, allowing shifting.
Systems of this type have long been applied to automotive applications. U.S. Pat. No. 2,231,876 to Belts; U.S. Pat. No. 2,247,164 to Butzbach; U.S. Pat. No. 2,387,891 to Elkin; U.S. Pat. No. 2,519,080 to Simpson; U.S. Pat. No. 2,741,350 to Dodge; French Patent No. 1,051,103 and German Patent No. 27 42 809 all describe such systems. Also, U.S. Pat. No. 3,481,223 to Fraser describes such a system specifically applied to a motorcycle transmission. In Fraser an electrical switch has a plunger which is actuated by a lever arm riding on a cam surface attached to the shifting drum of a motorcycle transmission. The cam has depressions corresponding to the various gear positions and raised surfaces elsewhere. When the shift drum is moved during a shifting operation the roller is raised activating the switch and interrupting ignition current. The system described requires installation within the transmission case of the motorcycle and once so installed is difficult to adjust. Further, only a single switch is used to determine the start and finish of a shift. Precise adjustment of both shift start and shift finish can be critical in minimizing un-powered time in racing.